Several tests of renal function are being conducted on rats treated once or repeatedly with a diverse group of chemical nephrotoxicants (biphenyl, carbon tetrachloride, mercuric chloride) to compare the relative sensitivities and versatilities of the various tests in detecting chemical nephropathy. In addition, quantitative urinalyses are being conducted serially on rats treated with known nephrotoxic chemicals to determine if refractoriness to kidney injury occurs during repeated (subacute, subchronic) dosing experiments. The primary purpose of this project is to evaluate the usefulness of various renal function tests in subacute and subchronic toxicity studies and to compare alterations in function to changes in microscopic renal morphology. A secondary purpose is to develop improved testing methodologies.